A meteor stream is composed of dust particles that have been ejected

1. The primary focus of the passage is on which of the following?

(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon

….incorrect, this passage doesn’t compare two scientific theories





(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon

….correct

…..at first I just think option(B) only partially correct, this is only about the former half of para1

SEE para1
……In the model, the particles were randomly distributed throughout a computer simulation of the orbit of an actual meteor stream….


…..“Conventional theories”( not new theoretical model), however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream.

However “I DIDN’T NOTICE THE LATER HALF OF OPTION(B)”, which accurately describes para2&3---meteor shower



(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research

….incorrect, here we doesn’t evaluate anything





(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them

….incorrect
This is an option which I thought is right at first


Whenever the Earth passes through a meteor stream, a meteor shower occurs.
----para2 is about natural phenomena


Para1 is about the introduction to meteor stream(a natural phenomena) and its movement led to the argument of new computer-model

Para2 insert “meteor shower” into para1’s view of “meteor stream”, though we can say para1&2 are both related, but the passage’s main focus doesn’t about how two phenomena related


The Geminid data between 1970 and 1979 shows just such a
bifurcation, a secondary burst of meteor activity being clearly
visible at an average of 19 hours (1,200,000 miles) after the first
burst. The time intervals between the bursts suggest the actual
Geminid stream is about 3,000 years old.
---- demonstrating a way to measure “them”, here the passage
only measure para2&3 rather than para1





(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data

---only partially correct, here in the passage we analyze data both computer modeling as well as actual phenomenon





2. According to the passage, which of the following is an accurate statement concerning meteor streams?


A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit. Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields.




(A) Meteor streams and comets start out with similar orbits, but only those of meteor streams are perturbed by planetary gravitation.

…incorrect
At first I choose this choice and cannot quite understand why its wrong
Its that, if you reason back from (C) could we understand the theorem behind
----if “Meteor streams are composed of dust particles derived from comets.”
----as the author mention in the passage that “meteor streams are perturbed by planetary gravitation.”
----generally speaking, comets will also perturbed by planetary gravitation.”



(B) Meteor streams grow as dust particles are attracted by the gravitational fields of comets.

para1
Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' “individual orbits” are perturbed by planetary gravitational fields.


notice the difference between sentence in para1 and the statement of (B), though they’re very similar, the sentence clearly indicates its dust particles’ “individual orbits” will influence the “planetary” gravitational field rather than “comet’s”




(C) Meteor streams are composed of dust particles derived from comets.
….correct

sentence in para1 clearly correspond to the statement of (C)
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities.



(D) Comets may be composed of several kinds of materials, while meteor streams consist only of large dust particles.

the article doesn’t hint anything about the composition of comet and meteor stream


(E) Once formed, meteor streams hasten the further disintegration of comets.

nowhere in the article mention the “hasten of the further disintegration of comets”



3. The author states that the research described in the first paragraph was undertaken in order to





(A) determine the age of an actual meteor stream

Its para2&3, not para1

(B) identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age

….correct



(E) show that a computer model could help in explaining actual astronomical data





4. Q. It can be inferred from the passage that which of the following would most probably be observed during the Earth's passage through a meteor stream if the conventional theories mentioned in line 18 were correct?

Conventional theories, however, predicted that the distribution of particles would be increasingly dense toward the center of a meteor stream. Surprisingly, the computer-model meteor stream gradually came to resemble a thick-walled, hollow pipe.




(A) Meteor activity would gradually increase to a single, intense peak, and then gradually decline.

….correct
Below is the new computerized model’s view, opposite to conventional one

Two brief periods of peak meteor activity during the shower would be observed, one as the Earth entered the thick-walled "pipe" and one as it exited.



(B) Meteor activity would be steady throughout the period of the meteor shower.
(C) Meteor activity would rise to a peak at the beginning and at the end of the meteor shower.
(D) Random bursts of very high meteor activity would be interspersed with periods of very little activity.
(E) In years in which the Earth passed through only the outer areas of a meteor stream, meteor activity would be absent.





5. According to the passage, why do the dust particles in a meteor stream eventually surround a comet’s original orbit?



(A) They are ejected by the comet at differing velocities.
….correct
A meteor stream is composed of dust particles that have been ejected from a parent comet at a variety of velocities. These particles follow the same orbit as the parent comet, but due to their differing velocities they slowly gain on or fall behind the disintegrating comet until a shroud of dust surrounds the entire cometary orbit.




(B) Their orbits are uncontrolled by planetary gravitational fields.
(C) They become part of the meteor stream at different times.
(D) Their velocity slows over time.
(E) Their ejection velocity is slower than that of the comet.



6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?





(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.

both theories does not think particles “be distributed evenly throughout any cross section of the stream”


(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.

????
Whenever the Earth passes through a meteor stream, a meteor shower occurs.

(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.

Only new computer-model rather than conventional theories


(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
….correct


(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.
….out of scope







7. It can be inferred from the last paragraph of the passage that which of the following must be true of the Earth as it orbits the Sun?


On new computer-model’s side
Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.




(A) Most meteor streams it encounters are more than 2,000 years old.
…..incorrect
Most meteor streams(this paragraph only talks about Geminid stream) it encounters are more than 2,000 years old.



(B) When passing through a meteor stream, it usually passes near to the stream’s center.
(C) It crosses the Geminid meteor stream once every year.
….correct

Thus we can infer the meteor stream’s age

(D) It usually takes over a day to cross the actual Geminid meteor stream.

….incorrect
…but it also can be 19 hrs or others

(E) It accounts for most of the gravitational perturbation affecting the Geminid meteor stream.




8. Which of the following is an assumption underlying the last sentence of the passage?


Has the predicted twin-peaked activity been observed for the actual yearly Geminid meteor shower? The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst. “The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old.”



(A) In each of the years between 1970 and 1979, the Earth took exactly 19 hours to cross the Geminid meteor stream.

…incorrect
The Geminid data between 1970 and 1979 shows just such a bifurcation, a secondary burst of meteor activity being clearly visible at an average of 19 hours (1,200,000 miles) after the first burst.

Every year between 1970-1979, “all exactly 19hrs”…..wrong
--we only know “average”, but we cannot say “all exactly 19hrs”, its too overgenerializtion




(B) The comet associated with the Geminid meteor stream has totally disintegrated.

….out of scope

(C) The Geminid meteor stream should continue to exist for at least 5,000 years.

….out of scope


(D) The Geminid meteor stream has not broadened as rapidly as the conventional theories would have predicted.

….incorrect
Here we’re not concerned with the rate of broadening

(E) The computer-model Geminid meteor stream provides an accurate representation of the development of the actual Geminid stream.
….correct



THIS IS A VERY TOUGH PASSAGE, if you're not major in astronological, you cannot quit grasp, in a very short time, the whole picture of what this passage really talks about, I try to use picture-visual rather than words to present this passage's idea by drawing a sketch attached below

VeritasKarishma GMATNinja please help me with Q-6

The passage tells us:
Astronomers have hypothesized that a meteor stream should broaden with time ... The researcher found, as expected, that the computer-model stream broadened with time.

So both agree that the meteor stream broadens with time.
So when Earth passes through older meteor streams (which are broader), it will experience longer duration meteor showers (since Earth will take more time to cross a broader meteor stream)

Hence,

6. The passage suggests that which of the following is a prediction concerning meteor streams that can be derived from both the conventional theories mentioned in line 18 and the new computer-derived theory?

(A) Dust particles in a meteor stream will usually be distributed evenly throughout any cross section of the stream.
(B) The orbits of most meteor streams should cross the orbit of the Earth at some point and give rise to a meteor shower.
(C) Over time the distribution of dust in a meteor stream will usually become denser at the outside edges of the stream than at the center.
(D) Meteor showers caused by older meteor streams should be, on average, longer in duration than those caused by very young meteor streams.
(E) The individual dust particles in older meteor streams should be, on average, smaller than those that compose younger meteor streams.

(D) is correct.

Hi VeritasKarishma

I'm confused but the question was <<...derived from both the conventional theories mentioned in line 18...>>..
How come you cite <<Astronomers have hypothesized that a meteor stream should broaden with time ... The researcher found, as expected, that the computer-model stream broadened with time.>> since it's not conventional theories's assumption...?

Please help me
Thank you !

Astronomers have hypothesized that a meteor stream should broaden with time ...

This is the conventional theory. It is what astronomers have hypothesised.

The researcher found, as expected, that the computer-model stream broadened with time.

This is what they found on the computer model so it is the computer derived theory.

Both agree on this point.

Thanks for your reply VeritasKarishma !
I see the structure that you mentioned, “Astronomers have hypothesis that meteor stream should broaden with time” is Main idea here and Conventional theory is supporting idea so the conventional theory = Astronomer’s hypothesis.

However, what drives me crazy is that each “broaden with time” and “dense toward the center” demonstrates opposite direction.
I don’t understand how something can broaden with time, becoming denser towards the center. That’s why I thought astronomers’ assumption and conventional theory’s assertion are different.... Moreover, there is “however” after the conventional theory, putting more weight on the idea that they are going opposite direction.... ?

Posted from my mobile device

'Broaden with time' and 'dense toward the centre' are not conflicting parameters.
Look at this stream. It is narrow at places (top and bottom of picture) and broader at others (centre of picture). The entire stream broadens with time.

Also, the stream could have a lot of particles in the centre and relatively fewer at the edges (not apparent in the picture).

Hey folks,

I had the pleasure of going through this passage recently. Here are some notes from my analysis - based on my understanding. Hoping this is useful for students.

Passage Analysis
- Meteor stream: made of dust particles ejected from a comet, at various velocities
- Some particles go faster, they move ahead of the comet, some particles go slower, they fall behind. Net effect: a shroud of dust surrounding the entire comet, forming a stream
- Astronomer's Hypothesis: meteor stream should broaden with time, because the dust particles’ individual orbits are impacted by planetary gravitation fields. This is the existing hypothesis (so, the conventional idea about this thing)
- Recent Computer simulation: done to test the above hypothesis (does a meteor stream broaden with time?)
- Simulation Result: Yes, meteor stream does broaden with time.
- Conventional Theory: Distribution of dust particles in a meteor stream - light at the edges, dense at the center (like the bell shaped curve in statistics - visualize)
- Actual Observation from the Model: Dense at the edges, light at the center (like a thick walled, hollow pipe)
- Whenever the earth passes through a meteor stream, a meteor shower occurs
- As per Model: If the stream were 5000 years old, earth would take just over a day (24 hrs) to cross the meteor stream, moving at 15L miles/day around the orbit of the meteor stream.
- As per Model: Two brief separate periods of peak meteor activity. This is like the earth cutting through the cross-section of a thick hollow pipe, - visualize. Dense/heavy at the entry and exit (peak meteor activity), light at the center. In other words: Model suggests thick hollow pipe theory, not conventional theory.
- Time interval between the 2 bursts varies (because the earth does not have to move through exact center - may/may not). Varies from one year to the next. Inference: This means earth going through a meteor stream is a yearly event.
- Actual Real life data supports the model i.e. model is accurate
- Thick walled hollow pipe is what is actually seen - 2 bursts of activity, 19 hours apart (not 24 hours). Dense at the extremes, light at the center.
- When the model used 5000 years as age at input -> greater than 24 hours (time); What we saw: 3000 years (actual) -> 19 hours. Suggests that Older the meteor, longer the duration of the meteor shower (visualize this: pipe with a larger diameter - takes longer for the earth to go through the cross section. Older meteor, longer duration).


Hope this helps create a better understanding of this passage.

Cheers!
Harsha

Question 7

Let's start with answer choice (C):
In the last paragraph, as you say, the author mentions the "yearly Geminid meteor shower." In the 2nd paragraph, we also learn that "whenever the earth passes through a meteor stream, a meteor shower occurs."

Because the Geminid shower happens once per year (yearly), and because a meteor shower occurs every time the earth passes through a meteor stream, we can conclude that the earth passes through the Geminid meteor stream once per year. So (C) is correct.

Let's consider (D):
The last paragraph tells us that the average time for the earth to pass through the meteor stream is 19 hours. This doesn't rule out the possibility that it usually takes more than a day, so (D) could be true. However, it's also possible that it usually takes less than a day. Since the question is asking which of the following must be true, (D) is incorrect.

I hope that helps!

Could anyone explain why D is wrong and E is correct?
I can't seem to understand why we have to assume that the computer model was correct

Question 8

Question 8 asks us for "an assumption underlying the last sentence of the passage."

That last sentence reads: "The time intervals between the bursts suggest the actual Geminid stream is about 3,000 years old."

The author provides the following evidence to reach this conclusion:

• Meteor streams spread out over time.
  
• A computer model predicted that a meteor stream would create a "hollow pipe" shape.
  
• It also predicted that, if the Geminid stream were 5000 years old, the earth would take "just over a day" to pass through the pipe. So, you'd have a bunch of meteor activity one day, and then a bit over a day later you'd have a bunch more meteor activity.
  
• In actual data, there was actually just under a day between peak meteor activity.

So, the actual data from 1970-1979 matches a narrower pipe than the one in the 5000 year old model. Because meteor streams get wider over time, this shows that the Geminid stream is younger than the model -- it's 3000 years old, not 5000 years old.

Which answer choice do we NEED to assume to reach this conclusion?

Here's (D):

"Conventional theories" predicted a pattern that is totally different than the "hollow pipe" pattern. According to these theories, you shouldn't have a first burst and then a second burst at all -- instead, you'd have only one peak meteor time.

But the data referenced in the last sentence DOES match the "hollow pipe" pattern. The author has pretty much thrown out the "conventional theories" altogether, and instead provides support for the "hollow pipe" theory.

Since the argument in the last sentence has nothing to do with the conventional theories, the author doesn't need to assume the information in (D).

Here's (E):

How does the author reach the conclusion that the Geminid meteor stream is 3000 years old? It all relies on the computer model. That model says that if it were 5000 years old, the pipe would be wide enough to cause over a day between bursts of meteor activity. Relative to this prediction, the actual data shows that the pipe is skinner, which means that the stream must be a bit younger than 5000 years.

Because the conclusion entirely depends on the computer's prediction, we NEED to assume that this prediction is accurate. Without that assumption, there is no support at all for the claim that the stream is 3000 years old.

The last sentence relies on the assumption in (E), so (E) is the correct answer to question 8.

I hope that helps!

KarishmaB GMATNinja

1.The primary focus of the passage is on which of the following?
(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon
(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data

Why B is correct and E incorrect?
I was confused between B & E.
For B, the first para explains the model and later actual data explained about the phenomenon.
I think E is incorrect because the model was constructed first and then data was explained and not vice-versa? Let me know if my reasoning is correct.


3. The author states that the research described in the first paragraph was undertaken in order to
(C) explore the nature of a particularly interesting meteor stream
(E) show that a computer model could help in explaining actual astronomical data

Why E is incorrect? I thought the model was the main focus of 1st para and model does help to explain the real data.
Can you help me understand the purpose of 1st para?

Thank you for your help!

Question 1.

Break down the passage. Main point of the 3 paragraphs:

Para 1 - Tells us that the computer model predicted a thick-walled, hollow pipe.
Para 2 - Discusses what should be observed if this is true.
Para 3 - Tells us that this is true! (with actual values observed)

1.The primary focus of the passage is on which of the following?

(A) Comparing two scientific theories and contrasting the predictions that each would make concerning a natural phenomenon

Conventional theory is also mentioned but no predictions are made about it.

(B) Describing a new theoretical model and noting that it explains the nature of observations made of a particular natural phenomenon

Correct. It describes the computer model and notes that the model explains the actual observations.

(C) Evaluating the results of a particular scientific experiment and suggesting further areas for research

No discussion on 'further areas for research'. Eliminate.

(D) Explaining how two different natural phenomena are related and demonstrating a way to measure them

Only one natural phenomenon discussed. Doesn't tell us how measurements are taken.

(E) Analyzing recent data derived from observations of an actual phenomenon and constructing a model to explain the data

This switches the order of the events. The computer model predicted a hollow pipe and the observations confirmed it. This option says that we first observed the data and then concluded that it must be a hollow pipe. That is not correct. The computer model predicted it and afterwards we observed the data and figured that it does support the hollow pipe hypothesis.

Answer (B)

Question 3.

3. The author states that the research described in the first paragraph was undertaken in order to

(A) determine the age of an actual meteor stream
(B) identify the various structural features of meteor streams
(C) explore the nature of a particularly interesting meteor stream
(D) test the hypothesis that meteor streams become broader as they age
(E) show that a computer model could help in explaining actual astronomical data

What is the "research" described in the first para?

From the passage:
Astronomers have hypothesized that a meteor stream should broaden with time as the dust particles' individual orbits are perturbed by planetary gravitational fields. A recent computer-modeling experiment tested this hypothesis by tracking the influence

The first para discusses the research conducted to support the hypothesis given by the astronomers. The research was the computer model. Why was the computer modelling done? To test the hypothesis.

Hence option (D) fits perfectly.
(D) test the hypothesis that meteor streams become broader as they age

(C) explore the nature of a particularly interesting meteor stream

The hypothesis and the research were done to identify the nature of the meteor streams in general, not the nature of a particularly interesting stream (Geminid's stream). Geminid was just chosen to experiment on as an example of a meteor. Hence incorrect.

(E) show that a computer model could help in explaining actual astronomical data

The modelling was done to test the hypothesis, not to show that modelling can explain data. It was found that the data obtained from modelling is actually observed in nature. Hence incorrect.

Answer (D)

Can anyone help explain Question 6?

Check this and the following posts: https://gmatclub.com/forum/a-meteor-str ... l#p2571607